docs: def concatenate(self, catalogue):
          """
          This method attaches one catalogue to the current one
  
          :parameter catalogue:
              An instance of :class:`htmk.seismicity.catalogue.Catalogue`
          """
  
          atts = getattr(self, 'data')
          attn = getattr(catalogue, 'data')
          data = _merge_data(atts, attn)
  
          if data is not None:
              setattr(self, 'data', data)
              for attrib in vars(self):
                  atts = getattr(self, attrib)
                  attn = getattr(catalogue, attrib)
                  if attrib is 'end_year':
                      setattr(self, attrib, max(atts, attn))
                  elif attrib is 'start_year':
                      setattr(self, attrib, min(atts, attn))
                  elif attrib is 'data':
                      pass
                  elif attrib is 'number_earthquakes':
                      setattr(self, attrib, atts + attn)
                  elif attrib is 'processes':
                      if atts != attn:
                          raise ValueError('The catalogues cannot be merged' +
                                           ' since the they have' +
                                           ' a different processing history')
                  else:
                      raise ValueError('unknown attribute: %s' % attrib)
          self.sort_catalogue_chronologically()